1. Field of the Invention
The present invention relates to an image display method and an image display apparatus, and more specifically, relates to an improved method and apparatus for displaying two or more images of an identical object.
2. Description of the Related Art
The technique of comparing two or more images of an identical object has been used in various fields to find differences between those images for, e.g., checking the object based on the difference.
For example, in the field of manufacturing industrial products, the above technique has been utilized to search those portions of a product where improvement in endurance is desired by comparing two images, one being an image of a new product and the other being an image of the same product after an endurance test, and finding those portions where great differences are observed between the two images. In the field of medical treatment, as another example, the technique has been used by doctors to follow progress of disease or stages of a cure and plan the most suitable course of treatment by comparing a plurality of radiation images of the same diseased part of a patient taken at different points in time.
When using the technique of comparing two or more images as is used on a daily basis in various fields, those two or more images are often displayed on an image display etc. Before displaying the images on the image display etc., the images are converted to image density signals or luminance signals.
When displaying two or more images to be compared, the images may be displayed either on a single image display or on a plurality of separated image displays. In either case, it has heretofore been common to display the images so that a position of an edge of the entire extent of one image, including the background in the image, is matched to positions of the edges of the other images. With such a manner of display, a location of the object in one image is also matched to locations of the object in other images only in the case where the image portion depicting the object always occupies the same overall location in the image.
However, the position or posture of the object may change between the images to be compared, especially when comparing images taken at long intervals. Such changes in the position or posture often occur particularly in medical images (such as radiation images of a patient), because the level of a camera stage is adjusted many times a day to be optimized to each patient, making it impossible to reproduce the previous level of the camera stage, which was adopted when a previous image of a patient was taken, when taking a new image of the same patient. Practically, it is also impossible to precisely reproduce the posture of the patient with respect to the central axis of the body etc.
Thus, the object (i.e., the region of interest or the region to be compared) in each image appears at an unmatched location when two or more images to be compared are displayed in the conventional manner (i.e., when the images are displayed so that the position of the edge of the entire extent of one image is matched to the positions of the edges of the other images), as the position or posture of the object usually changes between the images to be compared as described above.
It is difficult to compare two or more images correctly in the situation where the object (i.e., the region of interest) occupies different locations in the two or more images to be compared, which may cause the difference between the image portions depicting the object to be overlooked.